EP0260416A2 - Planare Wellenleitervorrichtung - Google Patents

Planare Wellenleitervorrichtung Download PDF

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Publication number
EP0260416A2
EP0260416A2 EP87110998A EP87110998A EP0260416A2 EP 0260416 A2 EP0260416 A2 EP 0260416A2 EP 87110998 A EP87110998 A EP 87110998A EP 87110998 A EP87110998 A EP 87110998A EP 0260416 A2 EP0260416 A2 EP 0260416A2
Authority
EP
European Patent Office
Prior art keywords
waveguide
substrate
refraction
index
buffer layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP87110998A
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English (en)
French (fr)
Other versions
EP0260416B1 (de
EP0260416A3 (en
Inventor
William C. Robinson
Norman A. Sanford
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Polaroid Corp
Original Assignee
Polaroid Corp
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Filing date
Publication date
Application filed by Polaroid Corp filed Critical Polaroid Corp
Publication of EP0260416A2 publication Critical patent/EP0260416A2/de
Publication of EP0260416A3 publication Critical patent/EP0260416A3/en
Application granted granted Critical
Publication of EP0260416B1 publication Critical patent/EP0260416B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/06—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 integrated waveguide
    • G02F2201/066—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 integrated waveguide channel; buried
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/07—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 buffer layer

Definitions

  • the present invention relates to optical communications and, more particularly, to planar optical waveguide devices for use as components in optical circuits.
  • Waveguide devices of various types including some mode converters, such as modulators, and switches requiring an input of electrical energy for their opera­tion, are needed to direct and control electromagnetic carrier waves in the optical region of the spectrum for conveying information.
  • Waveguide devices of planar con­struction have been found advantageous for many applica­tions because of their small size, durability, low cost and ease of fabrication.
  • the waveguide can be formed as a channel in a planar substrate of crystalline birefringent light propa­gating material by various methods to raise the index of refraction of a localized portion of the substrate.
  • Commonly used procedures for raising the index of refrac­tion of a light propagating material include ion exchange processes by which, for example, titanium is diffused at high temperature into the material or the material is immersed in a bath of melted benzoic acid.
  • the energy is applied through electrodes, normally in the form of thin strips of metal deposited on, over or near the wave­guide.
  • electrodes normally in the form of thin strips of metal deposited on, over or near the wave­guide.
  • One problem with the presence of metallic electrodes near the waveguide is that the guided waves are attenuated by the optical absorption of a portion of the energy of the waves in the vicinity of the electrodes.
  • a thin dielectric film for example, about 0.1 micron of silicon dioxide, having an index of refraction lower than that of the waveguide and then to deposit the metallic electrodes onto the dielec­tric film.
  • the dielectric film must be of high optical quality, that is, it must be free of defects such as impurities or occlusions that define light scattering centers which contribute to the attenuation of guided waves.
  • the dielectric layer must have an index of re­fraction equal to, or less than that of, the substrate, must also have a thickness sufficient to prevent the wave energy field from coming into contact with the electrodes, and an electrical conductivity sufficiently low, that is, a resistivity sufficiently high, to prevent current from passing into the substrate when electrical energy is applied at the electrodes.
  • waveguides formed with the foregoing processes tend to have asymmetric modal power distributions with respect to the axis of the waveguide. Due to this asymmetry, the coupling efficiency of light to and from these waveguides is greatly reduced.
  • a planar waveguide device is to protect optical waves in the waveguide of a planar waveguide device from attenuation by metallic electrodes by forming a buffer layer in the substrate of the planar waveguide device and forming the buffer layer by a pro­cess which can be precisely controlled and reliably produces a defect-free buffer layer.
  • Another object of the invention is to increase conductivity in the region of the substrate near the waveguide to reduce space charge accumulation and sub­stantially reduce optical damage effects.
  • the problems associated with isolating information-conveying optical carrier waves propagating through waveguides in planar waveguide devices from the attenuation caused by optical absorption of wave energy by metallic electrodes are overcome by providing in the substrate of the waveguide device a buffer layer of reduced index of refraction between the waveguide and the electrodes to optically isolate the waveguide from the electrodes.
  • the buffer layer is formed by applying a layer of magnesium over a substrate of x-­or y-cut crystalline birefringent material in which a waveguide has previously been formed and then oxidizing the magnesium at temperature for a predetermined time. Afterwards, the electrodes are deposited as required on the magnesium oxide buffer layer.
  • the MgO buffer layer has been found to facilitate optimizing the action of TE-TM mode conversion devices and to greatly reduce the sensitivity to D.C. bias fields used to force phase match TE-TM modes in such devices.
  • the buffer layer may alternatively be produced by an ion exchange, or proton exchange, process in a planar substrate of x-cut or y-cut crystalline birefrin­gent material having a waveguide formed substantially parallel to the z-axis as a localized region of raised index of refraction.
  • the ion exchange process actually lowers the ordinary index of refraction of the substrate in a stratum at the surface to define the buffer layer.
  • the buffer layer can be relied on to be uniform and homogeneous as well as having its index of refraction carefully controlled within limits.
  • the proton exchange process involves immersing the substrate in an acid bath such as melted benzoic acid at a prescribed temperature for a predetermined period of time. This permits the thickness of the buffer layer to be controlled precisely by adjusting the temperature and duration of the bath.
  • the buffer layer In addition to optically isolating the wave­guide from the electrodes, the buffer layer, formed with either technique, buries the waveguide below the surface of the substrate and is believed to make the power dis­tribution of the wave modes more symmetrical with respect to the axis of the waveguide thereby improving the efficiency of coupling between the waveguide and optical fibers.
  • An apparent advantage of the buffer layer is an increase in the electrical conductivity of the surface layer region of the waveguide, which permits the ionized impurities in the waveguide to migrate until their charges are neutralized. As a result, electrical charges are prevented from accumulating in the waveguide, and perturbations of the waves caused by charge accumulation are avoided.
  • a substrate 12 of high quality optical material such as an x-cut or y-cut crystalline birefringent material, has a localized region of increased refractive index to define a waveguide 14 along the z-axis.
  • the waveguide 14 can be formed by a number of processes, one of which is the in-diffusion of a transition metal, such as titanium. Electric potential is applied to the waveguide device 10 by leads 16 and 18 connected to electrodes 20 and 22, respectively, in the form of thin strips of metal deposited on or near the waveguide 14.
  • a thin layer 24 of high quality dielectric material for example, about 0.1 micron of silicon dioxide, has ordinarily been provided by sputter deposition on the substrate 12 between the waveguide 14 and the electrodes 20 and 22.
  • planar waveguide devices In planar waveguide devices according to the present invention, an exemplary example of which is a mode conversion device, identified generally by the reference numeral 11 in Fig. 2, a planar substrate 13 made of a crystalline birefringent material, such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), is cut in the x-or y-crystalline directions and has a waveguide 15 formed within acceptable limits substantially parallel to the z-axis.
  • a planar substrate 13 made of a crystalline birefringent material, such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3)
  • a magnesium oxide buffer layer 17 that overlies it, including waveguide 15, throughout its width.
  • a magnesium oxide buffer layer 17 On top of the buffer layer 17 are deposited three metallic electrodes, 19, 21 and 23 having leads 25, 27 and 29, respectively. Electrode 23 sits directly over waveguide 15, and electrodes 19 and 21 sit with their inboard edges adjacent the outboard edges of waveguide 15.
  • the channel waveguide 15 is formed by the indiffusion of a thin Ti stripe which is oriented parallel to the substrate z-axis.
  • TE and TM modes propagate with very nearly the same effective indices when both are well guided. This is the case since the Ti dopant increases the ordinary index of the material to faciltiate guiding for TE as well as TM modes.
  • Mode conversion is realized by placing the pair of electrodes, 19 and 21, parallel to and on either side of the channel waveguide 15, as well as the third electrode 23 directly on top of it.
  • the effective indices of orthogonally polarized TE and TM modes are forced to near equality by action of the r(12) and r(22) electrooptic coefficients.
  • electrode set 1 must sustain a bias voltage. In many instances, it would be impractical to apply such D.C. bias fields since they may lead to degradation of mode conver­sion behavior as well as time dependent drift in the characteristics of the device. Here, these effects are minimized by burying the waveguide and symmetrizing its axial index distribution.
  • the technique used in this embodiment to depress the index of the channel waveguide surface to symmetrize the index distribution involves diffusion of a thin layer of magnesium oxide into the surface of the substrate following waveguide formation.
  • the magnesium dopant acts as an index depressing agent and thereby cancels the effect of the titanium in raising the index of the guide surface.
  • Waveguides were formed in this geometry by diffusing into the substrate 400 A thick Ti stripes 3 microns in width at 1100°C for 5 hours. Following this initial diffusion, the substrate was coated with 230 A of Mg and returned to the furnace and oxidized at 900°C for 4 hours in flowing wet oxygen.
  • the resulting guide supported a single mode at a wavelength of .632 microns.
  • the three-electrode pattern was subsequently placed over the buried channel.
  • the center electrode was 5 microns in width and the gaps between center and outer electrodes was 5 microns. Electrodes were 12 mm in length.
  • the devices were tested for relative attenuation of the TE and TM modes prior to applying bias fields. No preferential loss in the TM mode was observed.
  • the guide was excited with TM polarized light and a bias of 14 volts was applied to the outer elec­trodes, 19 and 21. A 30 volt (pp) A.C. signal was applied to the center electrode. The throughput characteristic of the TE and TM modes were separately monitored.
  • Electrodes 36 and 38 are defined by thin strips of metal to which leads 40 and 42, respectively, are attached and are positioned on or near the waveguide 34.
  • a buffer layer 44 is provided directly in the substrate 32 to isolate the waveguide 34 from the metallic electrodes 36 and 38.
  • the waveguide 34 is formed as a localized region of raised index of refraction in the shape of a channel by the in-diffusion of titanium or other transition metal in connection with appropriate masking of the substrate 32 to define an intermediate product, as can be seen from Fig. 3.
  • the substrate 32 and its waveguide 34, having a raised index of refraction relative to the rest of the substrate, are subjected to a proton exchange, which, for the x-cut or y-cut material having the waveguide 34 substantially parallel to the z-axis, actually lowers the oridnary index of refraction of the material in a stratum at the surface.
  • the stratum of reduced ordinary index of refraction defines the buffer layer 44 between the waveguide 34 and the metallic electrodes 36 and 38, which are later deposited on the buffer layer 44.
  • the lowered ordinary index is effective in isolating the electromag­netic waves in the waveguide 34 from the electrodes 36 and 38 because both the TE and TM modes "see", that is, they are influenced by, the ordinary index of refraction in the crystalline birefringent material.
  • the ion exchange, or proton exchange, takes place by immersing the substrate 32 in a bath of melted benzoic acid, for example, at 250°C for three minutes to deplete the lithium from a stratum approximately 0.3 microns thick at the surface and thereby form the buffer layer 44, as can be seen from Fig. 5.
  • the ordinary index of refraction of portions 44a of the buffer layer 44 lying in the substrate 32 but outside the region exposed to the titanium in-diffusion is reduced below the ordinary index of the rest of the substrate by approximately 0.02.
  • the burying of the waveguide 34 is believed to help make the modal power distribution of the waves more symmetrical with respect to the axis of the waveguide 34 and, thereby, improve the efficiency of coupling between the waveguide and optical fibers. It is also believed that the proton exchange process increases the electrical conductivity of the surface of the waveguide 34, thereby making it easier for the ionized impurities in the substrate to migrate until neutralized and avoiding the perturbations of the visible wavelengths by charge accumulation near the waveguide.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)
EP87110998A 1986-09-15 1987-07-29 Planare Wellenleitervorrichtung Expired - Lifetime EP0260416B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US06/906,931 US4775208A (en) 1986-06-06 1986-09-15 Planar waveguide mode converter device
US906931 1986-09-15

Publications (3)

Publication Number Publication Date
EP0260416A2 true EP0260416A2 (de) 1988-03-23
EP0260416A3 EP0260416A3 (en) 1988-12-14
EP0260416B1 EP0260416B1 (de) 1993-04-28

Family

ID=25423244

Family Applications (1)

Application Number Title Priority Date Filing Date
EP87110998A Expired - Lifetime EP0260416B1 (de) 1986-09-15 1987-07-29 Planare Wellenleitervorrichtung

Country Status (5)

Country Link
US (1) US4775208A (de)
EP (1) EP0260416B1 (de)
JP (1) JPH083581B2 (de)
CA (1) CA1298390C (de)
DE (2) DE3785630T2 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2271192A (en) * 1992-09-01 1994-04-06 Ericsson Telefon Ab L M Optical switch

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FR2615006B1 (fr) * 1987-05-04 1991-10-04 Thomson Csf Guide d'onde optique integre, son procede de fabrication, et son utilisation dans un modulateur electro-optique
JPS6457207A (en) * 1987-08-28 1989-03-03 Hitachi Ltd Waveguide type optical device
US4984861A (en) * 1989-03-27 1991-01-15 United Technologies Corporation Low-loss proton exchanged waveguides for active integrated optic devices and method of making same
US5020872A (en) * 1990-01-04 1991-06-04 Smiths Industries Aerospace & Defense Systems Incorporated Method of operating an electrooptic modulator
US5359682A (en) * 1990-03-07 1994-10-25 Cselt-Centro Studi E Laboratori Telecomunicazioni S.P.A. Method of adjusting the operation characteristics of integrated optical devices
IT1240124B (it) * 1990-03-07 1993-11-27 Cselt Centro Studi Lab Telecom Metodo per ritoccare le caratteristiche di funzionamento di dispositivi ottici integrati.
IT1245961B (it) * 1991-05-10 1994-11-07 Alenia Aeritalia & Selenia Processo di fabbricazione di guide ottiche a canale in linbo3.
EP0620458A4 (de) * 1992-09-07 1995-02-01 Nippon Kogaku Kk Optisches wellenleiterbauelement und ein dieses verwendendes optisches instrument.
JPH06235833A (ja) * 1993-02-09 1994-08-23 Nikon Corp 光導波路
DE69415286T2 (de) * 1993-11-25 1999-05-06 Northern Telecom Ltd., Montreal, Quebec Polarisationwandler
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US5834055A (en) * 1995-08-30 1998-11-10 Ramar Corporation Guided wave device and method of fabrication thereof
US5749132A (en) * 1995-08-30 1998-05-12 Ramar Corporation Method of fabrication an optical waveguide
JP2850950B2 (ja) * 1996-01-19 1999-01-27 日本電気株式会社 導波型光デバイス
JP3425843B2 (ja) * 1996-09-30 2003-07-14 富士写真フイルム株式会社 光導波路素子の電極の形成方法
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2271192A (en) * 1992-09-01 1994-04-06 Ericsson Telefon Ab L M Optical switch
GB2271192B (en) * 1992-09-01 1996-10-09 Ericsson Telefon Ab L M Near Z digital switch

Also Published As

Publication number Publication date
CA1298390C (en) 1992-03-31
DE260416T1 (de) 1988-07-21
JPH083581B2 (ja) 1996-01-17
US4775208A (en) 1988-10-04
EP0260416B1 (de) 1993-04-28
JPS6375725A (ja) 1988-04-06
EP0260416A3 (en) 1988-12-14
DE3785630D1 (de) 1993-06-03
DE3785630T2 (de) 1993-08-05

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